Process of toning photographic silver-pictures.



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' No Drawing.

UNITED STATES PATENT OFFICE.

mmoLr rrscnnn, or's'rncnrrz; GERMANY.

rnocnss or 'I'ONIN-G rno'roenarnrc SILVER-PICTURES.

' Specification of Letters Patent. Patented Nov, 25, 1913, Application filed March 1, 1913. Serial No. 751,637. A

To all whom it ma concern:

. Be it known t at I, RUDoLr Fisormn, acitizen of the German Empire, and residing at Steglitz, near Berlin, Germany, have invented a certain new and useful Improved Process of Toning Photographic Silver- Pictures, of which the following is a specification. r

My invention relates to a process of toning and intensifying photographic silver- PlCtllI'ES. b

By the aid of suitable developers the la- .tent picture in photographic layers can be developed directly into acolored picture in so far as the oizidization products, which are formed when the latent picture is reduced, are colored and, owing to their physical or chemical properties, remain at the place where they are formed.- A yellowish-brown picture isfso obtained when developing with pyrogallol, a blue picture A with indoxyl, and a red one with thioindoxyl.

A primary objectof my invention is to obtain colored pictures of this kind not from the latent picture, but from a black developed picture.

I have found hat pictures which aredeveloped black can be converted into colored pictures with developers of this kind by first converting the sllver of suchpictures into reducible silver compounds by a method known per cc, 6. g. by potassium ferricyanidand potassium bromid,.and by then reducing such compounds with developers corresponding to requirements. In this case I obtain besides the silver picture a colored picture due to the colored oxidation product. In this manner it is possible subsequently toconvert any black s lver picture into a colored one. By repeating the operation new colored materials can be deposited at the places containing the silver, so that any desired intensification can be thereby obtained. Lastly, in order to obtain a pure colored picture the silver can be removed by one of the known reducing agents which will lighten the picture.

7 Fae ample.

1. A black silver picture is bleached in a solution of 10% potassium .ferricyanid and 10% potassium bromid, well diluted with water and then developed to a yellowishbrown color in a solution of 0.1 g. pyrogallol, 2 g. sodium carbonate and 100 c. cm. of water.

2. A picture bleached as described in Example'l is developed to a red color in a solution of 0.5 g. thioindoxyl carbonic acid, 5 0. cm. acetone, 2 g. potassium carbonate, and 100 0. cm. water.

I claim 1. The process of toning and intensifying photographic silver-pictures, consisting in first converting the silver in said pictures developing said pictures by developers ada ted to convert said compounds into oxidation products of the deslred color, said products remaining at the places where they are formed.

into reducible silver compounds, and then I In testimony whereof, I aflix my signature in the presence'of two witnesses.

' .RUDOLF FISCHER.

Witnesses;

HENRY HASPER, WOLDEMAR HAUPT. 

